The subject matter of the present invention relates generally to a veneer lathe apparatus and method for peeling sheets of wood veneer from a rotating log by means of a lathe knife and a nose bar which engages the side of the log immediately ahead of the knife, and in particular to an automatic control apparatus and method for automatic adjustment of the height of the nose bar above the lathe knife during peeling in response to reduction of the diameter of the log. In this manner, the two veneer exit gaps between the nose bar and the knife and between the nose bar and the knife backing member are automatically maintained at a width substantially the same as or slightly greater than the veneer path width which is equal to the thickness of the veneer plus a clearance space of a predetermined amount. This automatic control lowers the vertical height of the nose bar and positions the nose bar as close as possible to the knife thereby improving the quality of the veneer because such nose bar presses against the log closer to the knife to better back up and stabilize the wood surface of such log as it is being cut by the knife.
It has been proposed in U.S. Pat. No. 4,979,120 of Gary W. Ely, issued Dec. 18, 1990, to provide a veneer lathe with a computer control system for automatically adjusting the pitch angle of the lathe knife during peeling in response to changes in position of the knife carriage corresponding to a reduction in diameter of the log. The control system includes a digital computer having a memory in which a plurality of data tables are stored of different knife pitch angle profile ranges for different wood species. In this patent, the knife angle is adjusted by means of a cam follower roller which is adjusted in height by an eccentric relative to a pitch rail cam member along which the cam follower roller and associated knife carriage move during peeling. It was previously proposed in U.S. Pat. No. 4,708,180 of Browning et al., issued Nov. 24, 1987, to provide a veneer lathe system with an automatic knife gap adjustment during peeling by moving the nose bar of the lathe to different horizontal gap spacings between the knife and the nose bar during peeling by means of a computer control system in response to reductions in the log diameter and changes in knife pitch angle.
It has also been the practice previously to manually adjust the height setting of the nose bar relative to the knife blade to a predetermined position prior to peeling. However, previously there has been no automatic adjustment of the height of the nose bar relative to the lathe knife during peeling, as in the manner of the present invention. This prior lathe apparatus with manually set nose bar height has the disadvantage that the height of the nose bar relative to the knife must be set at a higher position than is necessary to provide a suitable veneer exit gap for small log diameters but such preset height position is higher than necessary for large log diameters. As a result the nose bar is positioned a greater distance from the knife than necessary when peeling large log diameters which reduces the quality of the veneer peeled from the log.
It has also been proposed in U.S. Pat. No. 4,893,663 of Gary W. Ely, issued Jan. 16, 1990, to provide a computer control system and method for automatic adjustment of the lathe knife pitch angle, the horizontal gap spacing between the nose bar and the knife, as well as the radial positions of the core drive rolls and back up rolls on the log in response to reductions in the log diameter and changes in the surface temperature of the log. However, there is no provision for automatically adjusting the height of the nose bar relative to the knife blade during peeling to improve the quality of the veneer in the manner of the present invention.
It has been discovered that it is desirable to position the nose bar at the lowest height position possible relative to the lathe knife in order to cause the nose bar to engage the log close to the knife to better stabilize the wood during cutting and thereby produce peeled wood veneer of higher quality. Therefore, in accordance with the present invention the nose bar height is adjusted while maintaining the two veneer exit gaps between the nose bar and the knife and between the nose bar and the knife backing member substantially the same as or slightly greater than the veneer peel path width which is equal to the veneer thickness plus a clearance space of a predetermined amount. The veneer lathe apparatus and method of operation of the present invention achieve this by automatically adjusting the vertical position of the nose bar relative to the knife during peeling in response to a control signal produced by a digital computer corresponding to changes in the position of the knife carriage and resulting reductions in the log diameter during peeling.
The veneer lathe apparatus and method of the present invention have several advantages over the prior methods and apparatus discussed above, including production of veneer of higher quality by automatic adjustment of the height of the nose bar roll during peeling with computer control system. The automatic control system enables a faster, easier and more accurate adjustment of the nose bar height while maintaining the veneer exit gap width substantially the same as the veneer peel path width which is equal to the veneer thickness plus a clearance space of a predetermined amount. This automatic control of the nose bar height also has the advantage of enabling the nose bar roll to be positioned closer to the knife during the entire peel so that a more uniform, better quality of veneer can be produced. In addition, the computer has data tables stored in its memory that include height adjustment curves of data points each comprising a data pair corresponding to the desired heights of the nose bar relative to the knife for different knife carriage positions and corresponding log radii. The data tables include a plurality of height adjustment curves for different log temperatures. In addition, since the data tables are stored in the computer memory they: can be changed easily by computer data entry to compensate for different wood species, different veneer thicknesses or other variables, such as knife pitch angle.
Another advantage of the present invention is simple, accurate and trouble-free adjustment of the height of the nose bar roll during peeling using a moveable wedge device that is operated by a computer-controlled cylinder. The movable wedge slides on a fixed wedge that is manually adjusted to a set position before the beginning of peel. These wedges are provided with suitable guides to control their movement and to maintain the relative lateral positions of the wedges. In addition, a resilient hold-down device is employed for mounting the nose bar roll support on the nose bar carriage to enable the height adjustment of the nose bar support during peeling while preventing lifting of the nose bar support which tends to happen as a result of rotation of the nose bar roll while it is engaged by the log. The resilient hold-down device is provided with a resilient bias in a simple, economical and trouble-free manner by using a pressure-regulated oil cylinder that allows a hold-down plate which engages the nose bar support to move up and down along a guide pin during height adjustment.